Several in vivo measurement systems are known in the art. They include swallowable electronic capsules which collect data and which transmit the data to a receiver system. These intestinal capsules, which are moved through the digestive system by the action of peristalsis, are used to measure pH (“Heidelberg” capsules), temperature (“CoreTemp” capsules) and pressure throughout the gastrointestinal (GI) tract. They have also been used to measure gastric residence time, which is the time it takes for food to pass through the stomach and intestines. These intestinal capsules typically include a measuring system and a transmission system, where a transmitter transmits the measured data at radio frequencies to a receiver system.
U.S. Pat. No. 5,604,531, assigned to the State of Israel, Ministry of Defense, Armament Development Authority, and incorporated herein by reference, teaches an in vivo measurement system, in particular an in vivo camera system, which is carried by a swallowable capsule. In addition to the camera system there is an optical system for imaging an area of the GI tract onto the imager and a transmitter for transmitting the video output of the camera system. The overall system, including a capsule that can pass through the entire digestive tract, operates as an autonomous video endoscope. It images even the difficult to reach areas of the small intestine.
FIG. 1 shows a block diagram of the in vivo video camera system described in U.S. Pat. No. 5,604,531. The system captures and transmits images of the GI tract while passing through the gastrointestinal lumen. The system contains a storage unit 100, a data processor 102, a camera 104, an image transmitter 106, an image receiver 108, which usually includes an antenna array, and an image monitor 110. Storage unit 100, data processor 102, image monitor 110, and image receiver 108 are located outside the patient's body. Camera 104, as it transits the GI tract, is in communication with image transmitter 106 located in capsule 112 and image receiver 108 located outside the body. Data processor 102 transfers frame data to and from storage unit 100 while the former analyzes the data. Processor 102 also transmits the analyzed data to image monitor 110 where a physician views it. The data can be viewed in real time or at some later date.
During a typical examination, the in vivo camera system may take anywhere from about four to eight hours or more to traverse the digestive tract. Assuming a capture rate of about 2 images per second, the total number of captured images can range from approximately 35,000 to 70,000 or more. If these images were subsequently displayed as a video sequence at a rate of 30 frames per second, one would require 20-40 minutes of viewing time to observe the entire video. This estimate does not include the extra time needed to zoom in and/or decrease the frame rate for a more detailed examination of suspect areas.
In some situations, the physician may desire to view only a portion of the video related to a certain anatomical structure. For example, if Crohn's disease is suspected based on symptoms such as abdominal pain, weight loss, iron deficiency anemia, diarrhea, an elevated erythrocyte sedimentation rate, or fever, then the in vivo camera system might be used to locate ulcerations within the small intestine. In this case, the physician may be interested in viewing only the segment of the video pertaining to the small intestine, and may not have the time or inclination to cue the video manually to find the beginning of the small intestine.
One remedy to this situation is to limit the capture frequency of the in vivo camera system until the capsule reaches the small intestine. For example, PCT Application WO 01/65995, assigned to Given Imaging Ltd., discloses a system for shutting down the imager and other device electronics for a period of approximately two hours until the capsule reaches the small intestine. This period of approximately two hours is derived solely from the known average motility of the human digestive tract. It does not rely on any patient specific information. Patient specific motility information can be used to adjust the capture frequency of the in vivo camera system, as is described in PCT Application WO 01/87377, also assigned to Given Imaging Ltd. However, neither average motility information nor patient specific motility information is enough to accurately pinpoint the anatomical structure or structures being captured in particular in vivo images or video segments.